H1N1 — the latest flu virus

In April of this year, a “new” flu appeared in the U.S. called novel H1N1 — a genetic combination of swine, avian and human influenza viruses.

H1N1, initially referred to as swine flu, is caused by influenza A viruses — the cause of worldwide pandemics — and spreads easily from human to human.

The symptoms are not particularly different from the seasonal flu viruses, nor are the treatment or precautions. But it has caused quite a media sensation.

First of all, it showed up in the spring — the flu season typically runs from November through March — and it never went away. It survived so well in warmer climates that the World Health Organization on June 11 declared it a pandemic.

Worst of all, there was no vaccination to fight it.

H1N1 has impacted all 50 states and at least 70 countries. Worldwide, according to the World Health Organization, more than 250,000 cases have been confirmed and roughly 3,000 deaths.

Currently in this country, 26 states are reporting widespread influenza activity.

Massachusetts has not been spared. Eleven people have died from flu-like symptoms — significantly less than the 78 in Florida, 81 in New York and 152 in California. Only four states so far have not confirmed deaths from H1N1 — Vermont, Idaho, and North and South Dakota.

The Boston Public Health Commission (BPHC) reports that almost 500 Boston residents have been diagnosed with H1N1 and 71 have been hospitalized. This virus has brought to light another issue — health disparities. The BPHC found that 75 percent of those hospitalized for flu-like symptoms have been black or Hispanic.

The reasons why are not clear, but it is thought that overcrowding in dense urban areas provides fertile ground for an aggressive virus. In addition, nationally, it has been determined that those with certain chronic illnesses are hospitalized at higher rates for H1N1. Such illnesses, like diabetes and asthma, are common in minority communities.

The impact has been noticeable — schools closed in its wake, public events were canceled and people in other countries did not venture outdoors without the safety of face masks.

The pattern of H1N1 demonstrates a sharp divergence from that of seasonal flu. While seasonal flu impacts the elderly disproportionately, H1N1 has spared that group. Experts theorize that those 60 and older have some immunity to the disease.

This time, the young are hit hard. The CDC has noted that the case rate is highest for those aged 5 to 24, and the hospitalization rate is highest for children up to the age of 4. Furthermore, 41 percent of deaths occurred in the 25-to-49 range.

Although the death rates have been higher in those with chronic diseases, seemingly healthy young people have not gone unscathed. This behavior has led schools and colleges to design strategies to control outbreaks.

There is good news to report. Vaccines against the virus are expected in October. Also, according to the National Institute of Allergy and Infectious Diseases, only one injection for healthy adults and children 10 and older may be necessary, and the protection takes effect more quickly than previously estimated. Most likely, children younger than 10 will need two shots administered 21 days apart. Further research is ongoing to determine the best number of inoculations for pregnant women.

The Commonwealth is doing its part to fight the H1N1 battle. Dentists, pharmacists and paramedics are now authorized to administer both seasonal and H1N1 vaccinations.

Mayor Thomas M. Menino convened the first-ever Boston flu preparedness summit in August, which resulted in a blueprint for containing the spread of influenza by identifying key steps that community partners, including businesses, schools, unions, health facilities and other sectors should take to keep residents healthy.

Although H1N1 is a very infectious disease, it can be contained in similar fashion to seasonal flu — get vaccinated; cover your mouth when you sneeze and cough; wash your hands frequently; and stay home if you’re sick. It also means that to effectively protect oneself from all types of flu this season, it is necessary to get at least two vaccinations.

The BPHC is also on target. They are partnering with members of the business sectors, unions, universities and colleges as well as health organizations to develop strategies in the face of an outbreak. One of their efforts is to not make it mandatory to bring in a doctor’s note if an employee is absent because of the flu. “We don’t want to overwhelm doctors with unnecessary visits and requests for notes,” said Dr. Nancy Norman, chief medical officer of the BPHC.

The CDC recommends staying home until a fever is not present without the aid of fever-reducing medicine for 24 hours. “We recommend that people stay home for four days after the first symptoms,” Norman said.

The flu can be managed at home without a doctor’s visit. “However, those of higher risk — pregnant women and those with chronic illnesses — should contact their doctor,” Norman advised. “It does not have to be a visit. A phone call will do.”

Older people and others at risk are advised to get two shots this year — one for seasonal flu and one for H1N1 flu.